Exhaust gas sensors may be used to control a variety of engine operating parameters. For example, U.S. Patent Application No. 2011/0132340 describes detection of exhaust gas water content using an exhaust gas sensor (e.g., a UEGO sensor), which is also used to control engine air-fuel ratio. However, during the duration in which the UEGO sensor is used to detect the exhaust water content, the sensor does not measure the exhaust air/fuel ratio. Therefore, during the water content detection period, the air/fuel controllability is lost.
The inventors herein have recognized the issues with utilizing an exhaust gas sensor to detect exhaust gas water content. Accordingly, embodiments for providing a dedicated exhaust gas water content sensor in an engine exhaust are provided. In one embodiment, a method for an engine comprises, based on a dew point of exhaust gas, adjusting an exhaust gas sensor heater configured to heat an exhaust gas sensor disposed in an exhaust passage of the engine, the dew point based on output from a humidity sensor disposed in the exhaust passage.
In this way, a humidity sensor in the exhaust passage of the engine may be used to determine the water content of the exhaust (and hence the dew point), rather than other exhaust gas sensors. By determining the dew point of the exhaust gas, the timing of activating the exhaust gas sensor heater may be adjusted to avoid rapid evaporation of condensate that has settled on the sensor when the dew point is greater than the temperature of the sensor, without compromising engine air-fuel ratio control. In some examples, the humidity sensor may also be utilized to determine the composition of the fuel used during combustion (e.g., ethanol and/or water content of the fuel) and the light-off temperature of a catalyst positioned in the engine exhaust. In doing so, accurate air-fuel ratio may be maintained even as fuel composition changes, and exhaust emissions may be controlled.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.